1. Field of the Invention
This invention relates to a magnetic recording medium and a process for producing the same. More particularly, the invention relates to a magnetic recording medium having high corrosion resistance and excellent runnability (capability to run smoothly), and a process for producing such magnetic recording medium.
2. Description of the Prior Art
As the anticorrosives used for the purpose of improving corrosion resistance of ferromagnetic metallic films of magnetic recording media, there have been proposed aromatic carboxylic acids having amino groups (Japanese Patent Application Kokai (Laid-Open) No. 58-194131), cupferrons (Japanese Patent Application Kokai No. 58-194138), polyamines (Japanese Patent Application Kokai No. 59-3724), benzotriazoles (Japanese Patent Application Kokai No. 58-194135), etc., some of which have been put to practical use.
There are various environmental factors, such as humidity, sulfur dioxide (sulfurous acid gas), nitrogen oxides, etc., which cause corrosion of ferromagnetic metallic films. None of the above-mentioned anticorrosives has a complete anticorrosive potency against these corrosive factors, and it can hardly be said that they show a satisfactory anticorrosive effect in use under the present-day complex corrosive environments.
When the ferromagnetic metallic film is covered with a higher-valent oxide which has a relatively high anticorrosiveness in itself, use of an anticorrosive having a reducing effect could prove detrimental to the protection of metallic film as such anticorrosive has an aptitude to break the anticorrosive oxide layer. In the prior art, however, little regard has been paid to such matter in the selection of anticorrosive.
Thus, various problems such as mentioned above have remained unsolved in the prior art regarding corrosion protection of ferromagnetic metallic films.
As a result of studies on the corrosion mechanism of cobalt-based ferromagnetic metallic films and the method for preventing corrosion thereof, the present inventors had previously found that when the surface of such ferromagnetic metallic film is mildly oxidized in the presence of oxygen and moisture to form a passivated cobalt layer which is essentially a cobalt oxyhydroxide layer containing three- or higher-valent cobalt ions, remarkable improvements can be attained in corrosion resistance, running stability and durability (Japanese Patent Kokai (No. 62-275316). It was found, however, that the provision of such passivated cobalt coat alone is insufficient to cope with the deterioration of corrosion resistance which would be caused when such cobalt layer is damaged due to takeup of dust or abnormal sliding contact against the magnetic head during running of the tape in actual use thereof.